Opposite spam problem

Opposite spam problem

Hello,

Fairly often, legitimate email is being marked as spam and put in the spam folder. When this happens, I go to the email and check the "+" next to the email address. This is supposed to put the email address in my address book and allow mail from that address through. What is actually happening is that I now have multiple address book entries for many of the same addresses, but email from them is still blocked about 50% of the time. This results in me missing timed offers, etc. How do I get this function to work properly?